Over the course of three days in San Francisco’s Golden Gate Park, nearly 100 bands take the stage at the free Hardly Strictly Bluegrass festival.

The festival began when Warren Hellman, a San Francisco banjo player and investment banker, approached city officials and local music impressario Dawn Holliday with the idea of bankrolling a one-day bluegrass festival in Golden Gate Park.

It has grown to include all kinds of music, yet one of the most rewarding aspects of the festival, held annually the first weekend of October, is that it brings back beloved musicians.

Organizers and fans alike call many of the regulars by their first names: Emmylou (Harris) is the “heart and soul” of the three-day festival, said Holliday, who curates the program.

Harris has been at every festival since it began in 2001 and traditionally closes it on Sunday evening.

Dave Alvin would be the songwriter laureate of California if such a position existed, Holliday said, and he’s back too.

“He is representative of California,” she said. For an older generation, “Merle Haggard was that. Dave is my Merle Haggard. He describes the lands of California, the hills, the valleys. And boy can he play that guitar.”

Hailing from Texas, Robert Earl Keen has become such a fan favorite, the festival moved him to a bigger stage this year.

“He’s a large person,” she said about Keen. “He lives large, he sounds large, and his bluegrass album last year was fantastic.”

Keen will be the final act Saturday on the Towers of Gold stage after outgrowing the Rooster stage, “so the audience can be that big too and match his energy,” Holliday said.

The first festival in 2001 was called Strictly Bluegrass and featured just a handful of bands. On the bill that year were Hellman favorites Emmylou Harris and Hazel Dickens (who died in 2011).

“We had no idea whether anybody would show up,” Hellman, then managing director of the San Francisco equity firm Hellman & Friedman, told The Press Democrat in 2010. “And there were 20,000 people.”

A couple of years later the festival expanded to include all sorts of musical styles and changed its name to Hardly Strictly Bluegrass.

Hellman died in 2011, just eight months after Dickens, but left a bequest that would enable Hardly Strictly to continue for many years.

He was “a truly beautiful one-percenter,” said Richard Koman of Santa Rosa, who regularly attends the festival.

Koman called Hardly Strictly “a living reminder of the spirit of the free Golden Gate Park concerts of the ’60s,” and said “seemingly a million people gather in the park without incident — it’s just a joyous celebration of the music and the city.”

There are seven stages, ranging from the capacious Banjo stage to the tiny Bandwagon platform. The Arrow stage is gone, Holliday said, because of sound bleeding over from Banjo.

Many festival mainstays who have been there since the early years “still hold the Warren feel,” Holliday said.

“It’s really important to me that Warren is still represented and loved. Emmy and Steve (Earle) and Robert Earl Keen all keep Warren in this. They have the history. They bring Warren back to the table.”